The present invention relates to a combined body of ceramics and metal used for, for example, turbocharger rotors.
A combined body of ceramics and metal used for turbocharger rotors or turbine rotors generally consists of a metal member P1 with a recess or through hole P2 which a ceramic member P3 is inserted into and engaged with as shown in FIG. 6.
On the combined body of such structure, however, a compressive force is applied onto an end of contact surface between the metal member P1 and the ceramic member P3, that is, an engagement end P4, and an extremely large stress is thereby concentrated on the ceramic member P3. Such extreme stress concentration unfavorably lowers the strength of the combined body. Furthermore, because of a large axial tractive force of the combined body, repeated load stress or thermal stress to the combined body causes fatigue and deterioration of the ceramics and drastically lowers the strength thereof.
Several methods have been proposed to relax the stress concentration or lower the axial tractive force by changing the shape or structure of the engagement end of the combined body or by surface treatment of the contact face with molybdenum disulfide; but they do not sufficiently solve the problems described above.
Examples of the former methods for relaxing the stress concentration include smoothing the engagement end of the contact surface between the ceramic member and the metal member before binding and forming a groove on the circumference of a sleeve on the engagement end (see Published Unexamined Japanese Utility Model No. Sho-61-176231). Such methods, however, require high working accuracy, increase working steps, and limit the degree of freedom for design.
The latter methods for relaxing the stress concentration include covering the combined body of metal and ceramics with a layer of molybdenum disulfide to reduce the frictional resistance. This method lowers an anti-torsional strength and an anti-slip off strength while relaxing the stress concentration. Although the long contact face may prevent the decrease of those strengths, the method increases the weight of the combined body and is not applicable to some parts such as turbochargers due to limitation of design.